Q BgQuestion:

      
Novice
Karma Points: 25
Respect (100%):
posted by  EE/MathMajor on 11/5/2009 12:19:59 AM  |  status: Closed  |  Earned Karma: 25

can figure it out

Course Textbook Chapter Problem Needs by
General Physics Fundamentals of Physics Extended (8th) by Halliday, Resnick, Walker 31 91 11/5/2009 at 6:00:00 AM
Question Details:
I've been working this problem for a few hours now and can't seem to figure it out. Please help me understand. 

The ac generator in the figure below supplies 120 V at 60.0 Hz. With the switch open as in the diagram, the current leads the generator emf by 27.5°. With the switch in position 1, the current lags the generator emf by 25.0°. When the switch is in position 2, the current amplitude is 4.50 A.
What are the following?
(a) R
Your answer is incorrect. 

(b) L
Your answer is incorrect. H

(c) C
Your answer is incorrect. F

Bonus Point Alert! Earn +4 additional karma points for helping this gold member.

AAnswers:

Answer Question Ask for clarification
(SME)
Moderator
posted by john_r on 11/5/2009 12:16:59 PM  |  status: Live
Asker's Rating: Lifesaver   
Response Details:


   from the given problem we can see that when the switch is open we have a series LRC circuit involving just the one
   caopacitor near the upper right corner so that we get
   [ωd L - (1 / ωd C)] / R = tanφo
                                       = tan (- 20o)
                                       = - tan20o

   now when the switch is in position 1 the equivalent capacitance in the circuit is 2C in this case we get that
   [ωd L - (1 / 2 ωd C)] / R = tanφ1
                                       = tan (10.0o)
   finally when the switch is in position 2 the circuit is an LC circuit with current amplitude
   I2 = εm / ZLC
       = εm / √[ωd L - (1 / ωd C)]2 
       = εm / [(1 / ωd C) - ωd L]
   where we use the fact that
   (ωd C)-1 > ωd L while simplifying the square root
(a)
   the resistance can be found from
   R = - εm / I2 tanφo
      = ....... Ω
(b)
   the inductance can be found from
   R = (εm / ωd I2) [1 - 2 (tanφ1 / tanφo)]
      = ....... H
(c)
   C = I2 / 2 ωd εm (1 - (tanφ1 / tanφo))
       = ............. F

Answer Question Ask for clarificarion

Join Cramster's Community

Cramster.com brings together students, educators and subject enthusiasts in an online study community. With around-the-clock expert help and a community of over 100,000 knowledgeable members, you can find the help you need, whenever you need it. Join for free today » How Cramster is different from tutoring »